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-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-
bounces@carnot.physics.buffalo.edu] On Behalf Of John Clement
Sent: Wednesday, December 15, 2010 5:10 PM
To: 'Forum for Physics Educators'
Subject: Re: [Phys-l] internal/external conservative/nonconservative
forces!?!?
You get energy by forming bonds, and it takes energy to stretch out
bonds,
so if you get energy by forming a bond the bond does not "contain"
energy.
If you associate energy with the system, then students are less likely
to
think that bonds "store energy". They are less likely to think that
breaking bonds gives you energy.
And the forces are all electromagnetic in chemistry, but how do you
transfer
the energy to the E_k of the individual molecules?? That is something
I
have never thought about with respect to forces, but using energy
considerations you know it happens.
Getting energy out of the system is a multistep process where you first
break bonds, and then make new bonds. So there is an energy barrier to
overcome.
The system concept is valuable because it promotes better thinking
about
bonds. It simply does not make sense to say something is in a
container
ready to be released when in reality you are taking it (energy) out
when
making the container (bond). Just try asking students whether energy
is
released or absorbed when a bond is broken, and I think you may be
surprised
at the answer.
John M. Clement
Houston, TX
student
If this energy shows up as KE of the byproducts, then I think a
could legitimately ask "What force accelerated these byproducts tothese
high speeds?" I don't see how associating energy with the systemversus
the bonds helps the understanding of the chemistry. Simply reciting athe
scenario where PE decreases and KE increases does not produce
understanding at a basic level - it's simply substituting a model for
dynamics. (This is why I became frustrated with Chemistry as anundergrad
- too much scenario in the introductory courses.)conservative/nonconservative
Bob at PC
-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-
bounces@carnot.physics.buffalo.edu] On Behalf Of John Clement
Sent: Wednesday, December 15, 2010 2:27 PM
To: 'Forum for Physics Educators'
Subject: Re: [Phys-l] internal/external
themforces!?!?
My example of bonds is very important to understanding chemistry.
Because
students will tell you there is energy in bonds and when you break
youyou
get energy. So if you dissociate gasoline the student will tell
thethat
releases energy. The student will tell you the same thing about
Krebslo.edu/mailman/listinfo/phys-l
cycle. This misconception blocks understanding of chemical and
physical
reactions.
_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l
_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l